1. Field of the Invention
This invention relates to the field sealing joints, more particularly, to the field of gaskets and methods for manufacturing them.
2. Description of the Prior Art
Various materials, such as cork, leather, rubber, plastic, and asbestos are used for the manufacture of gaskets. Of these materials, asbestos is most widely used for gaskets subject to extreme temperatures. However, asbestos gaskets tend to compress and laterally flatten under high temperature and pressure, resulting in leakage at the fitting which the gasket was intended to seal. To avoid leakage, the bolts of abutting flanges must be retorqued periodically to insure a fluid tight seal with the gasket, a time consuming process, especially where flanges are numerous and awkwardly located. More importantly, microscopic asbestos fibers which are inhaled are known to cause lung cancer. Thus, elimination of asbestos from the work environment is most desirable.
A superior replacement for asbestos gaskets are gaskets made from fluorocarbon polymers, for example, tetrafluoroethylene (TFE). However, by virtue of the present invention, the properties of fluorocarbon polymer gaskets are greatly enhanced when manufactured by hot coining. One of the advantages imparted to hot coined fluorocarbon polymer gaskets is their "living memory", a term which describes the gasket's expansion at elevated temperatures and the subsequent return to coined dimensions when cooled. At lowered temperatures, hot coined fluorocarbon polymer gaskets substantially retain their coined dimensions and flexibility. Further, creep or cold flow, defined as the total deformation of the gasket under stress after a period of time in a given environment beyond that initial strain that occurs immediately upon loading, is virtually eliminated. Thus, the need for retorquing flange bolts, loosened by gasket elongation or flattening between the flange faces in response to extremes in temperature and pressure, is eliminated by using hot coined fluorocarbon polymer gaskets having a "living memory".
Another advantage of hot coined fluorocarbon polymer gaskets is their ease of repair and reusability. A damaged fluorocarbon polymer gasket can be simply heated to its fluorocarbon polymer gel temperature after which it is hot coined anew. Also, since fluorocarbon gaskets experience no brittleness or deformation as a result of successive compression and recovery, they may be used repeatedly.
Additionally, fluorocarbon polymer gaskets are ideally suited for chemical applications since fluorocarbon polymers are corrosion resistant, nonsoluble, nonadhesive and nonflammable.
Finally, the carcinogenic asbestos health hazard is eliminated by substituting asbestos gaskets with fluorocarbon polymer gaskets.